Pulse oximeters are noninvasive, easy to use, inexpensive instruments for measuring the oxygen saturation level of arterial blood. Pulse oximeters reduce the risk of accidental death and injury by providing early detection of decreases in the arterial oxygen supply. As a result, pulse oximeters have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care units, general wards and home care. These instruments perform a spectral analysis of the pulsatile component of arterial blood so as to determine the relative concentration of oxygenated hemoglobin, the major oxygen carrying constituent of blood.
FIG. 1 illustrates a pulse oximetry sensor 100 having emitters 110, a detector 120, and an aperture 130. The sensor 100 is attached to a patient at a selected tissue site 10, such as a fingertip or ear lobe. The emitters 110 are positioned to project light through the blood vessels and capillaries of the tissue site 10, and the detector 120 is positioned so as to detect the emitted light as it emerges from the tissue site 10. The aperture 130 allows emitter generated light that is transmitted through and partially absorbed by the tissue site 10 to reach the detector 120, while excluding ambient light and other noise sources. A pulse oximetry sensor is described in U.S. Pat. No. 6,088,607 entitled “Low Noise Optical Probe,” which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.
FIG. 2 illustrates a pulse oximetry system 200 having a monitor 201 and a sensor 100. The monitor 201 has drivers 210, a controller 220, a front-end 230, a signal processor 240 and a display 250. The drivers 210 alternately activate the emitters 110 as determined by the controller 220. The front-end 230 conditions and digitizes the resulting current generated by the detector 120, which is proportional to the intensity of the detected light. The signal processor 240 inputs the conditioned detector signal and determines oxygen saturation along with pulse rate. The display 250 provides a numerical readout of a patient's oxygen saturation and pulse rate. A pulse oximetry monitor is described in U.S. Pat. No. 5,482,036 entitled “Signal Processing Apparatus and Method,” which is assigned to Masimo Corporation, Irvine, Calif. and incorporated by reference herein.